Force scientific notation in Blender GUI
Make a Scientific Notation Property Group.
As a workaround could set up a property group to handle scientific notation. Restricted to the significant digits of the float property, but allows to set the the power.
import bpy
from bpy.props import FloatProperty, IntProperty, PointerProperty
from bpy.types import PropertyGroup


class ScientificNotation(PropertyGroup):
    def get_num(self):
        return self.number *  pow(10, self.power)
    number : FloatProperty(min=-10, max=10)
    power : IntProperty()
    value = property(get_num)

bpy.utils.register_class(ScientificNotation)
bpy.types.Scene.foo = PointerProperty(type=ScientificNotation)

Layout with both number and power to set. Use the value property in calculation.  Could use a string property for the number, to get more sig digits.

Example of use in python console.
&gt;&gt;&gt; C.scene.foo.number = 6.62607004
&gt;&gt;&gt; C.scene.foo.power = -34
&gt;&gt;&gt; C.scene.foo.value
6.626070022583007e-34

See also  https://blender.stackexchange.com/a/134310/15543